Electro-Magnetic Interference (“EMI”) is a major concern in wireless communication systems. These systems transmit and receive electro-magnetic (“EM”) signals to communicate data. Examples of such systems include mobile phones, wireless data networks (e.g. networks conforming to IEEE standards 802.11a/b/g/n), and global position systems/sensors (“GPSs”). EMI can become a problem when high-speed circuitry is routed in close proximity to a radio receiver. In particular, a high-speed signal can cause the emission of EMI, and when such a signal is routed in close proximity to a radio receiver, the receiver can undesirably receive the interference along with the intended received radio signal, termed the “victim” signal. The signal that imposes the interference can be termed the “aggressor” or “aggressing” signal. Thus, EMI often degrades the signal fidelity of the victim signal and impairs the quality of the radio reception. Exemplary sources of interference sources can include, among others, a high-speed bus carrying data from a processor to a high-resolution display and a high-speed bus carrying data from a camera imaging sensor to a processor.
As an example, FIG. 1 illustrates the interference phenomenon in a mobile phone system 100 (along with a solution discussed below, in the form of an exemplary embodiment of the present invention), where a general/global system for mobile communications (“GSM”) radio receiver 105 can be aggressed by one or more interference sources. Specifically, FIG. 1 illustrates two such exemplary EMI sources 110, 120, each emitting and/or receiving interference 150. One EMI source is a high-speed bus 120 carrying data from a digital signal processing (“DSP”) chip 135 to a high-resolution display 140. The other EMI source is a high-speed bus 110 carrying data from a camera imaging sensor 145 to the DSP chip 135. The camera imaging sensor 145 could comprise lenses coupled to a charge coupled device (“CCD”), for example.
Increasing the data rate or bandwidth of each lane, conductor, or channel of the display and camera busses 110, 120 is often desirable. This desire may be motivated by (i) a need to support higher display/camera resolution, which entails faster throughput commensurate with increasing the number of image pixels and/or (ii) a desire to reduce the number of data lanes in the bus 110, 120, thereby involving an increase in the data rate on the remaining lanes to support the existing aggregate throughput. Thus, improvements in the display 140 or camera system 145 (e.g. higher resolution or condensed communication bus) can degrade the performance of the radio receiver 105 in the mobile phone system 100.
Furthermore, it may be desired to improve the radio reception of mobile phones, such as cellular phones, with existing display/camera and bus technologies, i.e. to facilitate reception of weak radio signals. In other words, improving reception of low-power signals or noisy signals provides another motivation to reduce or to otherwise address interference 150 or crosstalk. A weak radio signal might have less intensity than the noise level of the EMI 150, for example. Thus, it is desired to reduce the EMI 150 to facilitate reception of weaker radio signals or to enable operating a mobile phone or other radio in a noisy environment.
High-speed busses 110, 120 emitting, carrying, providing, imposing, and/or receiving interference can take multiple forms. For instance, in the mobile phone application described above, the bus 120 carrying the display data is often embodied as a “flex cable” which is sometimes referred to as a “flex circuit” or a “ribbon cable.” A flex cable typically comprises a plurality of conductive traces or channels (typically copper conductors) embedded, laminated, or printed on in a flexible molding structure such as a plastic or polymer film or some other dielectric or insulating material.
FIG. 2 illustrates several flex cables 200 any of which could comprise the data busses 110, 120 inside a mobile phone or another electronic device. (As discussed in more detail below, those flex cables 200 can be adapted to comprise an exemplary embodiment of the present invention.) The high-speed buses 110, 120 may also take the form of a plurality of conductive traces routed on a rigid dielectric substrate or material, such as circuit traces printed on, deposited on, embedded in, or adhering to a circuit board (“PCB”).
EMI 150 can also become problematic when two or more radio services are operated on the same handset. In this situation, the transmitted signal for a first radio service may interfere with the received signal for a second radio service. Such interference can occur even when two or more services utilize different frequency bands as a result of (i) the transmitted power of the first signal being significantly larger than the received power of the second signal and/or (ii) limited or insufficient suppression of sidebands in practical radio implementations. Consequently, a small fraction of the first, transmitted signal can leak into the second, received signal as interference.
A third source of EMI 150 can be circuits or circuit elements located in close proximity to a victim channel or radio. Like the signals on the high-speed buses 110, 120, signals flowing through a circuit or circuit component can emit EMI 150. Representative examples of circuit elements that can emit a problematic level of EMI 150 include voltage controlled oscillators (“VCOs”), phased-lock loops (“PLLs”), amplifiers, and other active or passive circuit components (not an exhaustive list).
One technique for actively addressing signal interference involves sampling the aggressor signal and processing the acquired sample to generate an emulation of the interference, in the form of a simulated or emulated interference signal. A canceller circuit subtracts the emulated interference signal from the received victim signal (corrupted by the interference) to yield a compensated or corrected signal with reduced interference.
Conventional technologies for obtaining a representative sample of the aggressor signal, or of the interference itself, are frequently inadequate. Sampling distortion or error can lead to a diminished match between the interference and the emulation of the interference. One technique for obtaining a sample of the aggressor signal is to directly tap the aggressor line. However, the resulting loss of power on the transmitted aggressor line is detrimental in many applications, such as in handheld radios, cell phones, or handset applications. Directly tapping into the aggressor line can also adversely impact system modularity.
The interference sampling system should usually be situated in close proximity to the source or sources of interference. This configuration helps the sampling system sample the interference signals while avoiding sampling the radio signal. Inadvertent sampling of the radio signal could result in the canceller circuit removing the victim radio signal from the compensated signal, thereby degrading the compensated signal. In other words, conventional technologies for obtaining an interference sample often impose awkward or unwieldy constraints on the location of the sampling elements.
For handset applications, the sampling system should be compatible with the handset architecture and its compact configuration. Radio handsets, such as mobile phones, typically contain numerous components that design engineers may struggle to integrate together using conventional technologies. Strict placement requirements of conventional interference sampling systems frequently increase system design complexity. In other words, conventional interference sampling systems often fail to offer an adequate level of design flexibility as a result of positioning constraints.
Another shortcoming of most conventional technologies for active EMI cancellation involves inadequate management of power consumption. An active EMI cancellation system may consume an undesirably high level of electrical power that can shorten battery life in handset applications. That is, EMI cancellation technology, when applied in a cellular telephone or another portable device, often draws too much electricity from the battery or consumes too much energy from whatever source of energy that the portable device uses. Consumers typically view extended battery life as a desirable feature for a portable wireless communication product. Thus, reducing power consumption to extend usage time between battery recharges is often an engineering goal, mandate, or maxim.
To address these representative deficiencies in the art, what is needed is an improved capability for addressing, correcting, or canceling signal interference in communication systems. A need also exists for a compact system for sampling an aggressor signal and/or associated interference in a communication system, such as a cellular device. A further need exists for an interference sampling system that affords an engineer design modularity and/or flexibility. Yet another need exists for a system that reduces or suppresses signal interference while managing power consumption. A capability addressing one or more of these needs would support operating compact communication systems at high data rates and/or with improved signal fidelity.